The present invention relates to a semiconductor device fabricating process, and more specifically to a method for removing a resist film and a deposition after a dry-etching is carried out using the resist film as a mask in a semiconductor device fabricating process.
In a semiconductor device fabricating process, a through-hole or others is formed by utilizing a lithography process. Ordinarily, after a patterned resist film is formed, a dry-etching is carried out using the resist film as a mask, and thereafter, the resist film is removed. Here, when the dry-etching is carried out, an etching residue and a resist surface hardened layer occur. It is an important technical problem to remove these deposits without damaging metal layers and semiconductor layers which constitute a semiconductor device. In the following, a prior art example for removing the etching residue and the resist surface hardened layer will be described on an example of a process for forming a through-hole on a copper interconnection.
As shown in FIG. 1A, a buried copper interconnection is formed. After an HSQ (hydrogen silsesquoxane file 1 is formed on a semiconductor substrate (not shown) on which circuit-components such as transistors are formed, a copper interconnection composed of a TaN film 2 (barrier metal film) and a copper film 3 is formed in the HSQ film 1 by using a Cu damascene process. Then, a silicon nitride film 4 and another HSQ film 5 are formed on the HSQ film 1 in the named order. Furthermore, a resist film 6 patterned to have a predetermined shape is formed on the HSQ film 5. Here, the silicon nitride film 4 has a film thickness on the order of 20 nm. The resist film 6 is constituted of for example a chemical amplification resist.
Next, the HSQ film 5 and the silicon nitride film 4 are dry-etched using the resist as a mask until the copper film 3 is exposed, so that a through-hole 7 is formed as shown in FIG. 1B. An opening diameter of the through-hole is on the order of 0.2 xcexcm. An etching gas being used is a fluorocarbon based gas. In this dry-etching, an etching residue 8, which is a reaction product of the etching gas and the copper film 3, is deposited on an inner wall surface of the through-hole. In addition, a resist surface hardened layer 9 is formed on the resist film 6. The resist surface hardened layer 9 is composed of a reaction product of the etching gas and a resist material, copper, etc., and is generally difficult to remove.
Thereafter, as shown in FIG. 1C, the resist film 6 is ordinarily removed by an oxygen plasma ashing while maintaining the substrate temperature at 150xc2x0 C. to 250xc2x0 C., and then, deposits such as the etching residue 8 and a resist residue 11 are removed by a wet treatment using a liquid remover.
The oxygen plasma ashing causes an active species such as oxygen radicals generated by a plasma discharging, to react with the resist resin activated by the heating. Thus, an organic resin, which is the base of the resist, reacts with the oxygen active species generated by the plasma discharging, to be broken down into a gas such as CO2 and H2O, with the result that the resist is removed from the surface of the substrate. When the active oxygen species and the oxygen ion species in the oxygen plasma chemically react with the organic resin in the resist, since a threshold temperature exists, it is necessary to maintain the resist at a temperature not less than a predetermined constant temperature, in order to perform the oxygen plasma ashing. For this purpose, it is an ordinary practice to maintain the substrate at a temperature in the range of 150xc2x0 C. to 250xc2x0 C. However, if the ashing is carried out at this temperature, oxidation proceeds from a surface of the copper film into the inside of the copper film, so that an oxidized region 12 is formed as shown in FIG. 1C. If the oxidized region 12 is formed, an interconnection resistance increases, and in addition, a contact resistance between the copper film 3 and a through-hole filling metal is also increased.
In order to avoid this problem, it may be considered to remove the resist film and the deposits by only a wet treatment using a resist remover liquid, without using the oxygen plasma ashing. FIG. 2 schematically illustrate a condition after the wet treatment is carried out. With this wet treatment, the resist film 6 and the etching residue 8 are removed, but the resist surface hardened layer 9 is not removed and still remains on the HSQ film 5. As mentioned above, since the resist surface hardened layer 9 is composed of the reaction product of the etching gas and the resist material, the copper, etc., it is difficult to remove the resist surface hardened layer 9 by the wet treatment using the resist remover liquid. If the resist surface hardened layer 9 remains, when an upper level interconnection is formed later, a defective deposition of a barrier metal film occurs, with the result that the yield of production is lowered.
As a method for avoiding the remains of the resist surface hardened layer 9 and also for preventing oxidation of the copper film 3, it is carried out to thicken the silicon nitride film 4 to form an etching stopper film and to form a through-hole by a two-step dry etching. This process will be described with reference with FIGS. 3A to 3F, 4, 5A and 5B.
Similarly to FIG. 1A, a buried copper interconnection as shown FIG. 3A is formed. However, the silicon nitride film 4 is formed to have a film thickness of about 50nm, which is larger than that in the example shown in FIG. 1A. This silicon nitride film 4 will be used as an etching stopper in a later step.
The HSQ film 5 is dry-etched using the resist 6 as a mask until the silicon nitride film 4 is exposed, so that a through-hole is formed as shown in FIG. 3B. An opening diameter of the through-hole is on the order of 0.2 xcexcm. As an etching gas, a gas is used which can etch the silicon oxide film at an etching rate higher than that for a silicon nitride film. After the etching, an etching residue 10 is deposited on an inner wall surface of the through-hole, and a resist surface hardened layer 9 is formed on the resist film 6.
Thereafter, the resist 6 is removed by an oxygen plasma ashing. At this time, a resist residue 11 remains on the HSQ film 5 as shown in FIG. 3C. After the ashing, a wet treatment using a resist remover liquid is carried out to remove the resist residue 11 and the etching residue 10, as shown in FIG. 3D. Then, the silicon nitride film 4 is dry-etched to expose a surface of the lower level interconnection 3, as shown in FIG. 3E. As an etching gas, a fluorocarbon based gas is used. At this time, an etching residue 8 is deposited on the inner wall surface of the through-hole. Succeedingly, the wet treatment using the resist remover liquid is carried out again to remove the etching residue, as shown in FIG. 3F. Thereafter, a barrier metal is deposited on an inner surface of the through-hole, and-a buried conducting film is deposited, and then, a surface is planarized. Thus, a multi-level interconnection is completed.
As mentioned above, if the method of thickening the silicon nitride film to use the thickened silicon nitride film as the etching stopper is utilized, it is possible to prevent the oxidation of the copper film 3 -to some degree. However, this method needs an increased number of steps, and in some cases, it is not possible to stop the dry etching at the silicon nitride film with good controllability, so that deterioration of the copper film 3 caused by the oxidation cannot be satisfactorily prevented. The reason for this will be described in the following.
When the lower level interconnection is formed of copper which is difficult to etch, a buried structure is ordinarily adopted, and an interconnection is completed by means of a Cu damascene process utilizing a CMP (chemical mechanical polishing) process. However, in the CMP process, there occurs a phenomenon often called a xe2x80x9cdishingxe2x80x9d in which a center portion of the copper film is recessed as shown in FIG. 4. This xe2x80x9cdishingxe2x80x9d is attributable to a difference in polishing rate between the barrier metal film and the copper film. If this xe2x80x9cdishingxe2x80x9d occurs, when the silicon nitride film 4 is formed on the HSQ film 1 having the lower level interconnection (2+3) formed thereon, the film thickness of the silicon nitride film 4 becomes thin at an edge of the copper film 3, as designated by the reference number 4A in FIG. 4. In some cases, particles generated in the CMP process remains in a recessed portion, so that a thinned portion occurs in the silicon nitride film 4 because of the remaining particles.
On the other hand, in the dry etching for forming the through-hole as shown in FIG. 3B, misalignment often occurs between the lower level interconnection and an opening formed in the resist film 6 as shown in FIG. 5A. When the misalignment occurs in a resist patterning, if the silicon nitride film 4 has the thinned portion as mentioned above, the dry etching cannot be stopped at the silicon nitride film so that the copper film is exposed as shown in FIG. 5A. In this case, an oxidized region 12 occurs in the copper film 2 as shown in FIG. 5B, with the result that an interconnection resistance increases, and in addition, a contact resistance is also increased.
Recently, with advanced microminiaturization of the semiconductor device, a so-called xe2x80x9cborderless interconnectionxe2x80x9d equalizing the width of an interconnection and the diameter of a through-hole, becomes widely adopted. Therefore, a damage of the copper film attributable to the misalignment becomes more significant.
Furthermore, when a plurality of through-hole having different opening diameters are formed, it becomes more difficult to stop the etching at the silicon nitride film. Since the etching rate becomes low in a through-hole having a small opening diameter because of a micro-loading effect, the dry etching becomes relatively rapid in a through-hole having a large opening diameter. Accordingly, when a plurality of through-hole having different opening diameters are formed in the same etching process, an overetching time in the through-hole having the large opening diameter becomes long, with the result that the etching of the silicon nitride film proceeds in the through-hole having the large opening diameter.
Because of the above mentioned circumstance, when the silicon nitride film is used as the etching stopper film, the silicon nitride film has to be formed to have a sufficient film thickness. Specifically, the silicon nitride film is required to have a film thickness of not less than 50 nm. However, if the film thickness of the silicon nitride film becomes large, a parasite capacitance between adjacent interconnections becomes large-because of a fringe effect. FIG. 6 illustrates a diagrammatic sectional view illustrating this phenomenon. As shown in FIG. 6, between an interconnection 50 and another interconnection 51 which are adjacent to each other in the same interconnection level, there exists a parasite capacitance 52 having an SiO2 film 54 as a capacitor dielectric film and another parasite capacitance 53 having a SiN film 55 as a capacitor dielectric film. Since the SiO2 film has a relatively low dielectric constant, the parasite capacitance 52 is relatively small. However, since the dielectric constant of the SiN film is about a double of the dielectric constant of the SiO2 film, the parasite capacitance 53 is relatively large. The magnitude of the overall parasite capacitance between adjacent interconnections is greatly influenced by the magnitude of the parasite capacitance 53. Therefore, when the film thickness of the SiN film 55 becomes large, the parasite capacitance between the interconnection 50 and the interconnection 51 remarkably increases, with the result that there occur various problems including a cross-talk.
As mentioned above, in the through-hole forming process, it was difficult to efficiently remove the resist film and the resist surface hardened layer while preventing the increase of the resistance of the copper film and the increase of the parasite capacitance between adjacent interconnections. However, when the through-hole is formed in a multi-level interconnection forming process, if any resist surface hardened layer remains, a barrier metal, which will be deposited later, will cause a defective deposition. Under this circumstance, a technology for efficiently removing the resist film and the resist surface hardened -layer without deteriorating the interconnection formed of the copper film.
Recently, it becomes much to form an interlayer insulating film of a low dielectric constant material such as an inorganic SOG (spin on glass), an organic SOG and HSQ in order to reduce the parasite:
capacitance between adjacent interconnections. However, these low, dielectric constant material has a problem in which if the low dielectric constant material is exposed to the oxygen plasma when the resist is removed, the dielectric constant elevates.
Accordingly, it is an object of the present invention to provide a method which has overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a method for removing a resist film and a resist surface hardened layer which is formed when a dry etching is carried out to expose an easily oxidizable film such as a copper interconnection and a low dielectric constant film after the films is formed, with giving no damage to the easily oxidizable film.
Still another object of the present invention is to provide a method for removing a resist film and a resist surface hardened layer, with giving no damage to a copper based metal film, in a process for forming a through-hole by means of a two-step dry etching using an etching stopper film such as a silicon nitride film, even if a thinned portion is generated in the etching stopper film and/or a misalignment of a patterned resist film occurs.
The above and other objects of the present invention are achieved in accordance with the present invention by a semiconductor device fabricating process including the steps of forming an easily oxidizable film on an insulating layer, forming a patterned resist film on the easily oxidizable film, dry-etching the easily oxidizable film using the patterned resist film as a mask to expose the easily oxidizable film, carrying out a plasma treatment using an non-oxidizing gas, and carrying out a wet treatment for removing the resist film and a resist surface hardened layer which was generated in the dry-etching.
According to another aspect of the present invention, there is provided a semiconductor device fabricating process including the steps of forming a copper-based metal film on an insulating layer, forming an insulating film on the copper-based metal film, forming a patterned resist film on the insulating film, dry-etching the insulating film using the patterned resist film as a mask to form a hole penetrating through the insulating film, carrying out a plasma treatment using an non-oxidizing gas, and carrying out a wet treatment for removing the resist film and a resist surface hardened layer which was generated in the dry-etching.
According to a third aspect of the present invention, there is provided a semiconductor device fabricating process including the steps of forming a copper-based metal film on an insulating layer, forming an etching stopper film on the copper-based metal film, forming an insulating film on the etching stopper film, forming a patterned resist film on the insulating film, dry-etching the insulating film using the patterned resist film as a mask to form in the insulating film an hole reaching the etching stopper film, carrying out a plasma treatment using an non-oxidizing gas, carrying out a wet treatment for removing the resist film and a resist surface hardened layer which was generated in the dry-etching, and removing the etching stopper film.
According to a fourth aspect of the present invention, there is provided a semiconductor device fabricating process including the steps of forming a patterned resist film on an insulating film which is formed of a material selected from the group consisting of HSQ, organic SOG and inorganic SOG, dry-etching the insulating film using the patterned resist film as a mask, carrying out a plasma treatment using an non-oxidizing gas, and carrying out a wet treatment for removing the resist film and a resist surface hardened layer which was generated in the dry-etching.
The above mentioned semiconductor device fabricating processes in accordance with the present invention, includes the dry-etching using the patterned resist film as a mask. Because of this dry-etching, the resist surface hardened layer is generated. As mentioned hereinbefore, the resist surface hardened layer is considered to be generated as the result of a reaction between the etching gas and a resist material, copper, etc., and is generally difficult to remove by a resist remover liquid. In the present invention, the plasma treatment using the non-oxidizing gas is firstly carried out, and then, the wet treatment is carried out, for the purpose of removing the resist film and the resist surface hardened layer. Why the resist surface hardened layer can be favorably removed, has not yet been necessarily clarified. But, it could be considered that, by means of the plasma treatment using the non-oxidizing gas, the resist surface hardened layer is broken and the change of properties occurs so that the resist surface hardened layer becomes a condition which can be easily removed by the resist remover liquid.
As seen from the above, the present invention is characterized by using the plasma treatment using the non-oxidizing gas, as a means for causing the change of properties in the resist surface hardened layer. Incidentally, an ashing method by a plasma treatment using a non-oxidizing gas, is known in the prior art (for example, JP-A-05-160022). However, this method is essentially different from the present invention in formation utilizing the plasma of the non-oxidizing gas.
First, in the present invention, the xe2x80x9ceasily oxidizable filmxe2x80x9d means a film which is easily oxidized if the film is exposed to an oxygen atmosphere, with the result that a characteristics inherent to the film itself is lost.
The xe2x80x9ceasily oxidizable filmxe2x80x9d can be exemplified by a copper based metal film. If the copper based metal film is exposed to an oxygen atmosphere, oxidation easily proceeds from the surface into the inside, with the result that, a low resistance, which is a characteristics inherent to the copper based metal film, is lost. Here, the copper based metal film means a metal film formed of copper or copper alloy. The copper based metal film is used as an interconnection film and a plug for connecting between different levels of interconnections. Here, the copper alloy can be exemplified by a copper/aluminum alloy. In this case, when the metal film is formed of the copper alloy containing the copper of not less than 90 weight %, an advantage of the present invention is remarkable. As known to persons skilled in the art, the copper based metal film can be formed by various processes, such as an electroplating, a sputtering, a CVD (chemical vapor deposition) process, etc. When the copper based metal film is used as the interconnection or the plug, the copper based metal film can be formed by the damascene process. Namely, a recess is formed at a predetermined portion of an interlayer insulating film, and a copper based metal film is deposited to fill up the recess, and then, an unnecessary portion of the copper based metal film is removed by for example a CMP process. Thus, the copper based metal film is formed in an interconnection pattern.
Furthermore, the xe2x80x9ceasily oxidizable filmxe2x80x9d can be exemplified by an insulating film formed of a low dielectric constant material such as HSQ, organic SOG and inorganic SOG. This type of low dielectric constant material can be said to be a typical example of the xe2x80x9ceasily oxidizable filmxe2x80x9d, because tie characteristics of the low dielectric constant is lost if this type of low dielectric constant material is exposed to the oxygen atmosphere.
The present invention can provide a technology for efficiency removing the resist film and the resist surface hardened layer while preventing oxidation of the easily oxidizable film. In the present invention, therefore, the easily oxidizable film includes various film which will lose its characteristics by oxidation. Accordingly, it should be understood that the above mentioned examples merely show a typical example of the easily oxidizable film, but the easily oxidizable film is in no way limited to only the above mentioned examples.
In the present invention, the non-oxidizing gas means a gas which does not substantially contain oxygen. For example, the non-oxidizing gas means can be defined by a gas having an oxygen content of not greater than 5000 ppm, preferably, not greater than 100 ppm. This non-oxidizing gas can be exemplified by hydrogen, ammonia, nitrogen, an inert gas, and their mixed gas. Among these gases, hydrogen, nitrogen and their mixed gas can be preferably used. Furthermore, the non-oxidizing gas is preferred to be a reducing gas which contains hydrogen. By using this type of non-oxidizing gas, it is possible to remove the resist film and the resist surface hardened layer while preventing oxidation of the easily oxidizable film. Here, the reducing gas can be exemplified by hydrogen or a mixed gas composed of hydrogen and at least one selected from the above exemplified non-oxidizing gases excluding hydrogen. For example, a mixed gas composed of hydrogen and nitrogen and/or an inert gas can be exemplified. When the non-oxidizing gas is the reducing gas which contains hydrogen, the hydrogen content is not limited from a theoretical view, but preferably,.is limited to 1 to 50 volume % if attention is paid to safety.
The flow rate of the non-oxidizing gas is suitably determined by considering the volume of a chamber in which the treatment is carried out, and in order to realize a stable plasma treatment. Ordinarily, the flow rate of the non-oxidizing gas is set on the order of 10 to 200 sccm (the flow rate of the whole of the mixed gas when the mixed gas is used). Incidentally, when the plasma treatment using the non-oxidizing gas is carried out in the present invention, a substrate temperature and a pressure are not limited. For example, the substrate temperature can be set at 50 to 250xc2x0 C., and the pressure can be set at not greater than 2 torr.
When the plasma treatment using the non-oxidizing gas is carried out in the present invention, an RF bias may or may not be applied to a semiconductor substrate. When the RF bias is applied, the semiconductor substrate is placed on an electrode connected to a high frequency power supply, and the plasma treatment using the non-oxidizing gas is carried out in a condition in which the RF bias is applied to the semiconductor substrate. In this case, bombardment of active species having a high energy occurs on the resist surface, to cause sufficient damage and change of properties in the resist surface hardened layer formed on the resist film, with the result that it becomes further easy to remove the resist surface hardened layer by use of a wet treatment using the remover liquid. The RE bias can be suitably determined dependently upon the type of plasma processing machine, but is ordinarily set to 10 to 50 W. If the RF. bias is too high, it is in some cases that the surface of the easily oxidizable film such as the copper interconnection and the low dielectric constant film is damaged. Incidentally, it is preferable to apply the RF bias in such a manner that the active species in the plasma is accelerated in a direction perpendicular to the substrate. From this viewpoint, when the RF bias is applied, the pressure is preferred to be set at as a low value as 0.1 torr to 1 torr.
A treatment time of the plasma treatment using the non-oxidizing gas depends upon the type of treating machine, but is set to be preferably 30 seconds to 10 minutes, more preferably 1 minute to 3 minutes. Incidentally, it is possible to remove the resist film by only the plasma treatment using the non-oxidizing gas, however, the removing rate is low so that a long time is required for removal. For example, when a chemical amplification resist is removed by only a hydrogen/nitrogen plasma treatment, the removing rate is on the order of 0.1 xcexcm/min
In the present invention, after the plasma treatment using the non-oxidizing gas is carried out, the wet treatment is carried out. This wet treatment is preferably carried out by using a resist remover liquid which uses amine compound, because it is possible to easily remove the resist surface hardened layer which was subjected to the plasma treatment.
In the present invention, the resist film can be formed -of various materials. In ordinary cases, a conventional resist material formed of an organic compound is used. For example, a novolak type of resist material or a chemical amplification resist material can be used. The chemical amplification resist material can be exemplified by a combination of a polyhydroxystyrene partially protected by a tertiary butoxycarbonyl group (abbreviated to xe2x80x9ct-BOCxe2x80x9d) and triphenyl sulfonium trifluorosulfonate (acid generating agent).
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.